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Polymers 2018, 10(5), 545; https://doi.org/10.3390/polym10050545

Lamellae Assembly in Dendritic Spherulites of Poly(l-lactic Acid) Crystallized with Poly(p-Vinyl Phenol)

1
Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya 60111, Indonesia
2
Department of Chemical Engineering, National Cheng Kung University, Tainan 701-01, Taiwan
3
State Key Laboratory of High-Efficiency Coal Utilization and Green Chemical Engineering, Ningxia University, Yinchuan 750021, China
4
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India
*
Author to whom correspondence should be addressed.
Received: 19 April 2018 / Revised: 8 May 2018 / Accepted: 14 May 2018 / Published: 18 May 2018
(This article belongs to the Special Issue Phase Behavior in Polymers)
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Abstract

Lamellar assembly with fractal-patterned growth into dendritic and ringed spherulites of crystallized poly(l-lactic acid) (PLLA), of two molecular weight (MW) grades and crystallized at (temperature of crystallization) Tc = 120 and 130 °C, respectively, are evaluated using optical and atomic-force microscopies. The results of surface-relief patterns in correlation with interior microscopy analyses in this work strongly indicate that the observed birefringence changes in PLLA polymer dendritic or ringed spherulites (from blue to orange, or to optical extinction) need not be definitely associated with the continuous helix twisting of lamellae; they can be caused by sudden and discontinuous lamellae branching at intersected angles with respect to the original main lamellae, as proven in the case of dendritic and zig-zag rough-ringed spherulites. Intersection angles between the main stalks and branches tend to be governed by polymer crystal lattices; for PLLA, the orthorhombic lattice (α-form) usually gives a 60° angle of branching and hexagonal growth. The branching lamellae then further bend to convex or concave shapes and finally make a 60–90° angle with respect to the main stalks. Such mechanisms are proven to exist in the straight dendritic/striped high-molecular weight (HMW)-PLLA spherulites (Tc = 120 °C); similar mechanisms also work in circularly ringed (Tc = 130 °C) HMW-PLLA spherulites. View Full-Text
Keywords: poly(l-lactic acid); birefringence; dendrites; ringed spherulites poly(l-lactic acid); birefringence; dendrites; ringed spherulites
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Siti, N.; Woo, E.M.; Yeh, Y.-T.; Luo, F.; Katiyar, V. Lamellae Assembly in Dendritic Spherulites of Poly(l-lactic Acid) Crystallized with Poly(p-Vinyl Phenol). Polymers 2018, 10, 545.

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